The present invention relates, in general, to kilns for drying wood, and, in particular, to a new and useful wood sample weighing method and apparatus which is used in a system for controlling at least one environmental parameter within the kiln.
It is known that by controlling the environmental conditions within the interior of a kiln, lumber positioned within the kiln may be dried at a controlled rate to minimize drying related defects of the lumber as it is dried. This includes conditions such as temperature, pressure, humidity and the like in steam, dehumidification, vacuum or other kilns.
In order to control the kiln temperature, humidity, or other condition, it was common practice for a sample piece of lumber to be selected from the stack of lumber being dried, and the moisture content of the sample was determined outside the kiln, at preselected intervals of time. With the moisture content information, the kiln temperature and humidity were altered, if necessary, to ensure that the lumber was dried at the desired rate.
The moisture content of the lumber sample was typically determined by this periodic removal of the sample from the kiln and by weighing of the removed sample or measuring some other characteristic of the removed sample to measure the moisture content. Such a process was time-consuming, susceptible to error and likely to effect the environment of the kiln interior since the kiln interior was exposed to ambient conditions during each removal of the sample from the kiln. The process was also uncomfortable and potentially dangerous in that the operator had to enter the hot kiln.
U.S. Pat. No. 1,593,890 to Welch, discloses an apparatus for drying wood which includes a balance beam for weighing a wood sample held in a horizontally extending position and at a non-disclosed location in a wood drying kiln. Nothing is mentioned in the reference on the survivability of the equipment within the corrosive, quickly-moving, hot, moist atmosphere in a kiln.
U.S. Pat. No. 5,325,604 to Little, discloses a system for use in the control of the environmental conditions, e.g. the temperature and humidity, of a kiln, based on a continuous determination of the moisture content in one or more wood samples in the kiln, which both circumvents the need for removing samples from the kiln and avoids the drawbacks of the Welch Patent. In the Little Patent the wood sample is suspended in a fixture adjacent an interior wall in the kiln which also contains the charge or stack of wood being dried. The fixture or sensor unit, contains a sensor in the form of an electronic load cell or strain gauge which measures force by generating an electric signal which is proportional to the force applied to the sensor. The fixture in the Little Patent requires an area of free wall space. U.S. Pat. No. 5,325,604 to Little is incorporated here by reference, in particular for its teaching of the structure and function of a kiln and the environmental control units therefor.
U.S. Pat. No. 5,775,003 to Goodwin, III, discloses a sensor for measuring the weight of a wood sample in a kiln while the sample hangs in a tunnel which partly encloses the sample. The tunnel is suspended on the wood charge in the plenum.
U.S. Pat. No. 5,226,241 to Goodwin, III, U.S. Pat. No. 4,176,464 to Randolph, U.S. Pat. No. 3,744,144 to Weis, and U.S. Pat. No. 3,131,034 to Marsh, disclose other methods and apparatuses for controlling wood drying kilns, including systems which weigh the entire lumber charge to determine its moisture content.
A need remains for further improvements in this field.
The present invention is not limited to the drying of any particular type of lumber or even any particular type of drying kiln but can be used for any kiln of any design and for drying any product.